1. Field of the Invention
This invention relates to a fuse, more particularly to an improvement of a fuse of the type which is used in vehicles such as automobiles to protect electrical power circuits therein in which relatively large amount of electric current flows.
2. Description of the Prior Art
In a vehicle such as an automobile, electrical power is usually supplied from a battery mounted therein, and various fuses are disposed to protect the battery from shorts. In particular, in an electrical circuit of an automobile in which relatively large amount of electric current flows, a fuse of the type as described in FIGS. 1 and 2 is generally used to protect electrical equipments and an electrical power source from a burning caused by excessive electric current.
Specifically, as shown in FIGS. 1 and 2, said known fuse 10 comprises a housing 11 of heat resistant synthetic resin and a fuse element 12 disposed in said housing 11, a pair of fuse contacts 13 and 13 each connected at one end thereof to both ends of the fuse element 12, respectively. The other ends of the fuse contacts 13 and 13 are protruded through a bottom plate 11a of the housing 11 outside in parallel with each other when assembled. Cable terminals 14 and 14 each attached to the end of a wire are connected to the fuse contacts 13 and 13, respectively, by fastening means such as a bolt.
In such a fuse 10, usually a housing cover 15 is attached on an upper opening space of the housing 11 to protect the fuse element 12 from external substances such as suspended dusts or the like which is apt to damage the fuse element, so that the inside of the housing is generally kept airtightly. Therefore, the inside of the housing 11 is apt to become high temperature by a heat generated by electric current flowing through the fuse element 12. Because of this, as a material which forms the housing 11, a heat resistant synthetic resin such as a nylon resin reinforced by fiberglass is usally used.
In the fuse as described above, the fuse element 12 is in an instant melted if excessive electric current flows therethrough. On the oher hand, if the amount of electric current is relatively smaller than that of the excessive current, the time required for melting the fuse element 12 (hereinafter referered to a "melting time") becomes long. The relationship between the magnitude of the electric current and the melting time is indicated by the line "A" in FIG. 3. As shown in the drawing, when an electric current I.sub.1 (hereinafter referred to as "non-melting electric curent") which is slightly larger than the rated current I.sub.o flows in the fuse-element 12, the fuse element 12 does not melt although it is heated and the generation of the heat is continued. As a result, the inside of the housing 11 becomes high temperature, so that there were disadvantages that thermal deformation may be caused in the housing 11 by an external force or an accident that only a part of the fuse element is melted may be happened.